This invention relates to film cabinets and, more particularly, to a film cabinet for storing and moving continuous loop film.
For many years, film has been stored on reels that rotate to unwind the film for feeding through a projector and subsequent rewinding onto a take-up reel. This reel-to-reel system of film transport though the projector generally has been regarded as satisfactory for feature length films shown a few times per day. However, when the film length is only several hundred feet and the film is shown continuously many times a day, such as in theaters, amusement parks and theme park attractions, for example, the reel-to-reel system has not been satisfactory. Perhaps the biggest drawback with these systems is the labor costs and time required to rewind and rethread the film. Furthermore, the film must be wound on top itself as the take-up reel pulls the film through the projector. This applies stresses to the film and frictional forces between overlapping strips of film that cause undue wear of the film. As a consequence, the film wears out very quickly, resulting in poor film quality and requiring frequent film replacement. This can be very expensive. Other disadvantages of the reel-to-reel system include the fact that the length of film that can be stored on the reel is limited by the size of the projector and diameter of the reel. If more than one reel is required to store the film, then two projectors are required to make a smooth transition from one reel to the next without interruption of the show or image projected. Rewinding of the film also is required, creating further wear.
To solve the problems associated with reel-to-reel storage and use of film, such as those described above, continuous loop film cabinets have been developed. These cabinets are designed to store and move a continuous loop of film throughout the cabinet, through a projector external to the cabinet, and then back to the cabinet itself. Because the film is in the form of a continuous loop, it never is wound on top of itself. Instead, the film is wound around rollers positioned at predetermined locations throughout the cabinet and driven around the rollers by a plurality of drive sprockets having teeth for engaging the perforated edges of the film. This substantially reduces premature film wear and maintains film quality for a much longer time than reel-to-reel systems. Moreover, excessive film length usually is not a problem, because the cabinets can be made relatively large and, if necessary, several cabinets may be employed back-to-back to store and move the continuous loop film through the cabinets and the projector.
While the continuous loop film cabinets are a big improvement over reel-to-reel film systems in continuous run applications, they are not without their own drawbacks. A typical film cabinet is about four feet wide, six feet tall and several feet deep. Thus, one significant drawback is that the cabinets are quite large, and sometimes several cabinets must be employed to store one loop of film. This drawback is especially troublesome in projector rooms where space oftentimes is very limited.
Another fundamental problem with existing film cabinets is the manner in which the film is directed and pulled through the cabinet. For example, in one known type of film cabinet, several parallel rows of drive sprockets are connected to the ceiling of the cabinet, with a plurality of free hanging rollers positioned in parallel rows in the lower region of the cabinet to receive the lower loops of the film as they come off one drive sprocket and go to the next drive sprocket. Both the drive sprockets and the free hanging rollers are relatively large and occupy valuable space within the cabinet. Consequently, the adjacent vertical strips of film are not very close to each other, because of the relatively large diameters of the sprockets and free hanging rollers. Furthermore, since the rollers at the bottom of the cabinet are suspended by the film without bearings, and thus hang freely in the film loop, they rotate as the film moves through the cabinet. As a result, several rows of drive sprockets must be utilized to pull the film through the cabinet. This takes up a lot of cabinet space. The free hanging rollers also are prone to falling out of the loops from which they are suspended, especially during cabinet movement. This creates further undesirable problems.
Another disadvantage found in some existing film cabinets is the lack of any provision to promptly cut power to the drive sprockets in the event that the film breaks or becomes accidentally unwound inside the cabinet. Thus, if the film breaks or becomes unwound, it will still be driven by the drive sprockets until it is totally unwound. The process of repairing and rethreading the film in the cabinet is very time consuming and, if the film becomes extremely tangled or otherwise damaged, it may not be possible to reuse the film, thus resulting in undesirable film replacement expenses.
There also is a lack of an effective and simple means for directing the film from the cabinet, for example, to the projector when the two units are not precisely aligned with each other. When the alignment is off, the film must twist and bend in order to be properly fed into the projector. When the film is being run at relatively high speed, it is very important that the film transfer be accomplished in such a manner so as to prevent excessive wear, unwinding, and damage to the film.
A further consideration in all film projection systems is the ease of maintenance and repair of the system. In the prior art film cabinet discussed above, there are several undesirable features which create difficulty in maintenance and repair. For example, the rows of drive sprockets in one known cabinet are rotated in unison by a lubricated chain drive system that tends to drip lubricant on the film and is messy, expensive and difficult to maintain. The continual cleaning, relubrication, checking of chain tension and other attention to the chain drive system makes it a maintenance nightmare. Film wear through various sources, such as the projector gate and elsewhere in the cabinet, creates a fine powder that is attracted to the film by static electricity from film movement in the cabinet. Airborne dirt from several other sources, including the rollers and other moving parts in the cabinet, also is attracted to and builds up on the film and produces what resembles a black snowstorm when the film is viewed on a screen. The labor and expense to clean the film and cabinet to maintain the quality of the image projected on the screen can be enormous. This also is due in large part to the fact that the rollers and other components of the cabinet are inconvenient and difficult to remove. The static electricity also causes the vertical strips of film to be attracted to each other, thus requiring further spacing between the strips and a waste of valuable cabinet space.
Accordingly, there has existed a definite need for a film cabinet that can store and move the maximum amount of film in the smallest space possible. There also has existed a need for a film cabinet that minimizes film damage if the film breaks or becomes unwound during operation, and that enables reliable high speed transfer of film between cabinets or between the cabinets and the projector or other device. Furthermore, there has existed a need for a film cabinet that is reliable in operation and simple and inexpensive to maintain. The present invention satisfies these needs and provides further related advantages.